Handling of liquefied gases



June 1, 1954 J. KOBOLD HANDLING OF LIQUEFIED GASES Filed Aug. 30, 1950/n ve n for:

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Patented June 1, 1954 HANDLING OF LIQUEFIED GASES Josef Kobold,Furstenfeldbruck, Germany, as-

signor to Maschinenfabrik Esslingen, Esslingen,

Germany Application August 30, 1950, Serial No. 182,331

Claims priority, application Germany September 6, 1949 1 Claim. 1

This invention relates to liquefied gases and more especially to thehandling of gases which are cooled to low temperature and stored inliquefied condition.

Liquefied carbon dioxide, cooled to low temperature, has been stored inlarge, well insulated low-pressure tanks, but difliculties have beenencountered when filling the intensely cooled lowpressure liquid fromsuch a tank into portable containers such as for instance steelcylinders. The cylinders must first cool down to the temperature of thestored liquid and during this stage great losses are caused byevaporation. Owing to the rise in pressure the continuous passage of thestored liquid into the cylinder through the narrow valve passages isinterrupted or at least greatly hindered.

It has been tried, although without complete success, to overcome thesedifiiculties by the use of one or several intermediate containers withequalization of pressure which, for the purpose of speeding up thebottling, are temporarily placed under higher pressure, but this way ofproceeding complicates matters and it has also been found that onconveying the intensely cooled low-pressure liquid through long pipes,pressure drop occurring in narrow passages may lead to a completeclogging-up by freezing, as frequently happens with carbon dioxide.

To prevent this, carbon dioxide in gas form has been evacuated from thetop of the low pressure tank by suction and liquefied anew by the normalhigh pressure method, to be then filled into the steel cylinders or putdirectly to some practical use such as the production of Dry Ice.

As a rule, liquefied carbon dioxide is stored under a pressure of 12 to15 atm., i. e. at a temperature of 36 to 30 C. below zero. Whenevacuating the carbon dioxide gas from the top of the tank, there arisesgradually a pressure drop accompanied by an evaporation of the storedliquid. Since owing to the insulation of the tank no entrance of heatworth speaking of is possible, the heat for evaporation is abstractedfrom the stored liquid until the pressure and temperature drop to thetriple point which for carbon dioxide lies at 5.26 atm. and 56 C. belowzero. The carbon dioxide then starts freezing and snow forms in the lowpressure tank. This point, which forms the lowest limit of thisevacuating procedure, is reached under the conditions aforementioned,after about 15-20% of the actual content of liquid carbon dioxide havebeen evacuated in gas form. Then one must wait until after some daysthrough the gradual entrance of heat the pressure in the low-pressuretank has risen correspondingly. Thus only a fraction of the gascontained in the tank is efiectively available under this procedure.

It is an object of this invention to improve the process hereabovedescribed.

It is another object of the invention to provide improved means for thecarrying out of the process modified in accordance with this inventionwhich does away with the overcooling of the liquid carbon dioxide andthe ensuing pressure drop in the storage tank by replacing the requiredevaporation heat by the heat of compression and condensation of thehighly compressed evaporating gas evacuated by suction. This manner ofproceeding retains all the advantages of the low-pressure storage, whilethe difiiculties mentioned above which are connected with the filling ofthe overcooled liquid carbon dioxide or other gas under low pressure areavoided. Obviously this constitutes an important improvement of thelow-pressure storage and filling into cylinders of liquefied gases. Inaddition to this, the liquefied gas also reaches the cylinders inabsolute purity, for all impurities remain in the low-pressure storagetank.

In the drawings afilxed to this specification and forming part thereoftwo embodiments of an installation adapted for carrying out the newprocess according to this invention are illustrated diagrammatically byway of example.

In the drawings:

Fig. 1 illustrates the provision of a low-pressure storage tank with acooler or condenser arranged inside the tank, while,

In Fig. 2 the cooler or condenser which at the same time serves as anevaporator for the tank liquid, is arranged outside of the tank.

Referring to the drawings and first to Fig. l, the fluid carbonic acidor other liquefied gas under high pressure, in order to be stored in thetank I, is passed from the compressor or a high pressure reservoir (notshown) through a supply pipe 2 and control valve 3 to be expanded to thestorage pressure of about 12 to 15 atm. In this operation part of thecarbonic acid liquid evaporates and passes as a gas under the samepressure through the shut-off valve A and return pipe 5 to thecompressor 6 to be there compressed again to the normal liquefactionpressure of -75 atm., according to the temperature of the cooling water.This highly compressed carbonic acid is then passed through valve i intothe condenser 8 cooled with normal cooling water and is lique- I liedagain therein, to be then re-introduced by way of the valves 9 and intothe supply piping 2 and to be passed together with fresh liquid carbonicacid, through the regulating valve 3, to expand in the tank 1 to storagepressure.

This is the known way in which the storage tank is charged. Alternatelythe returning gas after having been liquefied again, may be fed throughvalve H and pipe l2, to the normal filling station or to the place wherethey are intended to be put to use, so that only part of the freshliquid carbonic acidis stored under low pressure.

The low-cooled liquid carbonic acid stored in the low-pressure tank I,can now be tapped in the known manner directly by conducting it throughthe pipe 13 and valve I4 to the place of use, this operation beingaccompanied by the difliculties mentioned above, caused by highlosses byevaporation and by a clogging of the pipes and valves, or indirectly byevacuating the carbon dioxide in gas form by suction from the top of thestorage tank i through valve 4 and pipe 5, the gas to be then compressedfurther to a high pressure in the compressor 6 and to pass through valveI to the condenser 8. In the condenser the highly compressed gas isliquefied again with the aid of cooling water and the liquid carbonicacid is conducted under high pressure through valves 9 and H and pipe 12to the place of consumption. As mentioned above, this known processinvolves the drawback that of the carbonic acid stored in the lowpressure tank only a fraction can be tapped each time, since it willsoon be stopped by becoming frozen.

According to the invention, now, the difiiculties arising during theknown tapping proceedings are avoided by installing, according to Fig.1, in the low-pressure storing tank I a pipe coil or pipe system l insuch manner that it is surrounded by the low-cooled liquid in the tank.The exhausting and cylinder-filling is then carried through in thefollowing manner: the compressor 6 evacuates through the pipe 5 andvalve 4 from the top of the storage tank the quantity of carbonic acidgas corresponding to its handling capacity, compressing it again to thenormal high liquefaction pressure and forcing the gas under highpressure into the pipe system 15, the gas being cooled by the low-temcperature liquid in the tank and liquefied. During liquefaction acorresponding part of the tank liquid evaporates without the tank liquidbeing overcooled or the storage pressure dropping further. tank liquidand the quantity of high-pressure carbonic acid condensed in the pipesystem 15 approximately balance each other, since the heat ofcompression and the heat of condensation to be abstracted per unit areabout equal to the heat of evaporation required per unit. Thecomparatively small difierences which may still exist, can be soregulated by partial pre-cooling in the condenser 8 or a correspondingsubdivision The evaporating quantity of low-cooled of the cooling surfacof the system of pipes I5, that regardless of a continuous abstractionof gas from the storage tank the pressure and temperature in the tank ismaintained up to complete exhaustion, and clogging by freezing of theliquid from the tank is avoided. On the other hand it is now possible tomore or less overcool the carbon dioxide re-liquefied in the pipe systeml5 and to conduct it at the high pressure in the compressor through thevalve [9 to the steel cylinders or to the Dry-Ice station or to anyother place of consumption.

It is equally possible to introduce the fresh, highly compressed liquidcarbonic acid supplied through pipe 2 from the carbon dioxide producingstation directly through the valves [0 and I8 into the pipe system, tothere overcool it and to pass it through valve Hi to a place ofconsumption, whil the evaporation gas from the low pressure tank isliquefied again in the manner above described by means of the compressor6 and condenser 8.

The mode of operating the filling of the liquid in the tank intobottles, as illustrated in Fig. 2,.

differs from the one described with reference to Fig. 1 only by the factthat a vertical tank la is provided and the cooling and condensing pipevsystem I5 is not arranged inside, but outside of the low-pressurestorage tank, the evaporation of the tank liquid occurring in a separateevaporator 20, which the tank liquid enters by way of the valve 2| whilethe evaporation gas escapes through the pipe 22 and is conducted towardthe compressor 6 for another compression and reliquefaction.

Various changes may be made in the details of operation above describedwithout departing from the invention or sacrificing the advantagesthereof.

I claim:

Apparatus for transferring low-cooled liquefied gases from low-pressurestorage containers to apoint of consumption, comprising in combination,a storage container containing liquefied gas under low pressure, acompressor, a suction pipe leading from the part of said container abovethe liquid therein to said compressor, a cooling and condensing pipesystem communicating with the liquid space of said container, a pressurepipe conducting the gas compressed in said compressor into said pipesystem and a pipe leading from said pipe system to a point ofconsumption.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,371,427 Kerr Mar. 15, 1921 2,059,942 Gibson Nov. 3, 19362,379,215 Brinkman June 26, 1845 2,466,863 Phillips Apr. 12, 19492,499,404 Marsh Mar. '7, 1950 2,608,070 Kapitza Aug. 26, 1952

